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Calling their climate survey of 3,146 earth scientists the largest ever, researchers reported Monday that 82 percent of those surveyed agreed that human activity has been a significant factor in changing temperatures across the globe.

The researchers at the University of Illinois contacted or tried to contact 10,257 experts listed in the 2007 edition of the American Geological Institute's Directory of Geoscience Departments. More than a third responded to the survey late last year.

The two key questions asked were:

Among sub-groups, 97 percent of climatologists active in research agreed that humans play a role.

"The debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes," the researchers stated in summarizing their findings in the journal EOS.

Petroleum geologists and meteorologists were among the biggest doubters. Only 47 and 64 percent, respectively, believe in human involvement.

"The petroleum geologist response is not too surprising, but the meteorologists' is very interesting," lead survey author Peter Doran said in a statement released with the survey. "Most members of the public think meteorologists know climate, but most of them actually study very short-term phenomenon."

He was not surprised, however, by the climatologists. "They're the ones who study and publish on climate science," he said. "So I guess the take-home message is, the more you know about the field of climate science, the more you're likely to believe in global warming and humankind's contribution to it."

The survey was conducted online by experts who were e-mailed invitations. Computer IP addresses of participants were recorded and used to prevent repeat voting, Doran and fellow researcher Maggie Kendall Zimmerman noted.

They added that the questions asked were reviewed by a polling expert who checked for bias in phrasing, such as suggesting an answer by the way a question was worded.

While the number of experts taking the survey may seem low, Doran said it was in line with the nature of surveys, especially an online one. "These are very busy people," he said in citing possible reasons for not taking it. "People mistake it for junk mail. People think it's not legit. Some of the addresses may be inactive."

"We were actually very pleased with the response based on what we were told to expect," he added.